Center for Clinical Veterinary Medicine, Ludwig Maximilian University, Munich, Germany
Over the last 15 years, veterinarians are increasingly faced with the problem of ureteral obstruction in cats. Osborne et al. 2009 described a tenfold increase in upper urinary tract stones over the last 20 years.1 The higher incidence of upper urinary tract stones is complicated by the fact that the vast majority of these stones are calcium oxalate stones for which medical dissolution is not an option. If they do not pass spontaneously and instead cause obstruction, diversion of urine is warranted. Stones are the most common cause of ureteral obstruction (65–80%) followed by ureteral strictures (ca. 20%).2 Other less common reasons are dried solidified blood calculi that can also not be managed by medically dissolution, bladder neoplasia that obstruct urine outflow, accidental ligation of the ureter and in rare cases obstruction of the ureter with inflammatory products in cases of pyelonephritis.
Ureteral obstruction can be partial or complete, unilateral or bilateral. Studies in dogs have shown that complete ureteral obstruction decreases the renal blood flow to 40% within the first 24 hours and to 20% within two weeks.3 The GFR declined permanently to 65%, 56%, and 0% after 7, 14, and 40 days, respectively. If both ureters are completely obstructed, this will be fatal within 48 to 72 hours.4 In another experimental study investigating partial ureteral obstruction in dogs, relief of obstruction after 7 days, 28 days, and 60 days, resulted in recovery of GFR to 100%, 35%, and 8%, respectively.5 These are experimental studies in dogs with no preexisting azotemia. Many cats that are presented with ureteral obstruction due to ureteroliths already have compromised renal function due to CKD. Treatment should, therefore, be implemented as soon as possible to avoid further damage to the obstructed kidney. Unilateral obstruction leads to compensatory hypertrophy of the contralateral kidney. Such a compensatory response is, however, not possible in cats with preexisting CKD or in cats with bilateral ureteral obstruction.
Clinical signs in cats with ureteral obstruction are anorexia, lethargy, and vomiting as a consequence of acute uremia. Other clinical signs are weight loss, polydipsia/polyuria, signs of abdominal pain, vocalization, hematuria, and pollakiuria. On physical examination, cats show signs of abdominal pain and the kidneys are typically asymmetrical with one kidney enlarged and painful and the other kidney being small and irregular in shape (“big kidney - little kidney” presentation). Bilateral renomegaly is less common and can be identified in cases of bilateral ureteral obstruction. Cats with unilateral partial obstruction and good functioning of the second kidney can be asymptomatic.2,6,7
Most cats with ureteral obstruction are azotemic even when unilateral obstruction is present.2,6,8 This is certainly also due to the fact that more than 50% to 70% of cats have preexisting chronic kidney disease. In addition to azotemia, metabolic acidosis, hyperphosphatemia, and varying degrees of hyperkalemia can also be seen. A complete blood count shows anemia in two thirds of affected cats.8 A urinalysis including a urine culture should be performed in all cats. If the bladder is empty due to bilateral ureteral obstruction, a urinalysis and culture can be performed using urine obtained from the renal pelvis during surgical intervention.
The diagnosis of ureteral obstruction is based on physical examination findings and confirmed by diagnostic imaging of the abdomen. Abdominal ultrasound is the primary imaging method and should be performed in all cats with suspected ureteral obstruction. Ultrasound also allows to evaluate the intrarenal architecture, geometry and to assess whether chronic alterations are present. In addition, ultrasound can be used to monitor the treatment response by evaluating the renal pelvis and ureter size after medical and surgical intervention. Plain abdominal radiographs should be performed in all cats to look for radiodense stones in the kidney and ureter and for renal asymmetry. In 20–30% of cats no discrete calcified material is identified with ultrasound or plain abdominal radiographs. In these cases, antegrade pyelography can be performed to evaluate the patency of the ureter and to identify non-radiodense material in the ureter and ureteric strictures. In the author’s facility this is usually performed immediately before an interventional therapy. Contrast CT and MRI can also be used to evaluate ureteral patency.
Treatment options include medical treatment, traditional surgery, ureteral stent implantation, and subcutaneous ureteral bypass.
Medical treatment includes fluid therapy, diuresis with mannitol, analgesia, symptomatic treatment of uremic signs, and amitriptyline or alpha-sympatholytic drugs (e.g., tamsulosin or prazosin). Medical treatment has been shown to be effective in only around 10% of cats. If medical treatment is not successful after 24 to 48 hours, or if the patient is unstable (hyperkalemic, oliguric, overhydrated) immediate intervention is indicated to decrease the intrarenal pressure and to reestablish urine flow. During medical management, the renal pelvis should be checked for further enlargement.
Traditional surgery on feline ureters which have a diameter of only 0.4 mm is technically demanding. Perioperative mortality rates of 21% and perioperative complication rates of 30% have been reported.9,10 The most common complications of ureteral surgery are peri-operative leakage, stricture formation, and recurrent obstruction, which are observed in around 40% of cats with ureteral stones.
Interventional techniques with surgical assistance for renal decompression and reestablishment of urine flow such as ureteral stents and the subcutaneous ureteral bypass device (SUB) have been developed in the last decade and have improved the prognosis for cats with ureteral obstructions.
With the placement of feline double pigtail ureteral stents urine is diverted from the renal pelvis to the urinary bladder. The success rate of stent placement in a study with 69 cats (79 obstructed ureters) was 96%.2 The peri-operative mortality was 7.5%. Procedural complications were seen in 6/69 cats (urine leakage, pollakiuria/stranguria), postoperative complications (<1 week) in 6/66 cats (stanguria, pollakiuria, urine leakage, stent dislodgement), short-term complications (<1 month) in 6/61 cats (stranguria, pollakiuria, stent migration) and long-term complications in 20/60 cats requiring a stent exchange or SUB device in 19/60 cats. The median survival time was 498 days, and the 1-year survival rate of all stented patients was 65%. In another study with 26 cats (31 obstructed ureters) the mortality rate before discharge was 15%. In this study, obstructions were due to ureteric calculi (21 cats), ureteric strictures (4 cats), and due to traumatic bilateral obstructions (1 cat).11 Eight of the cats that survived to discharge were later euthanized due to marked azotemia, and three cats were euthanized due to severe dysuria refractory to medical treatment. In 8 cats, stent replacement was necessary due to stent migration, fracture, mineralization causing luminal obstruction, or sterile cystitis. The median survival time in this study was 265 days and the 1-year survival rate was 44%. Based on this study, the prognosis of cats with stent placement remains guarded because of the presence of chronic renal disease but also because of intervention related complications, such as dysuria, which is seen in up to 35% of cats with ureteral stents, stent migration, or fracture.
The SUB system includes a nephrostomy tube and a cystotomy tube, which are placed permanently and are connected via a subcutaneously placed shunting tube. With this system, urine can flow through the attached catheters from the renal pelvis to the bladder. Implantation of a SUB device was originally developed as a salvage procedure for cats in which a stent could not be placed due to a very narrow lumen of the ureter or excessive ureteral stones. In recent years, it has been shown that the SUB device is advantageous over stents for all causes of ureteral obstruction in cats with regard to mortality and long-term complications. In a retrospective study of 137 cats with ureteral obstruction due to ureterolithiasis (67%), stricture (13%), stricture and stones (20%), or pyonephrosis (0.5%) placement of the SUB device was successful in all cases. Peri-operative complications were device leakage (3.4%), kinking (5%), occlusion with blood clots (7.5%), and catheter mineralization (25%). Of the 137 cats, 94% survived to discharge and the median survival time was 827 days.12 Dysuria which is a common complication in cats with ureteral stents (>30%), is an uncommon complication in cats with an SUB device (<5%). A smaller study that investigated initial outcomes and complications of the SUB procedure at two university hospitals reported a need for blood transfusion in the peri- or postoperative period in 8/19 cats, pleural effusion in 2/19 cats, and a 21% rate of bacterial urinary tract infections within 10 days of surgery.13 None of these cats had a positive culture or an active urine sediment before surgery. Two patients had recurrent multi-drug-resistant UTI infections. Recurrent and resistant infections and the potential for biofilms are, therefore, a significant concern in SUB patients. The median disease-free interval was 180 days, the 1-year survival rate was 83%.
Ureteral obstructions in cats are increasing in frequency. Adequate diagnostics should be performed as soon as possible in order to identify this condition and to improve the chance for recovery of renal function with earlier intervention. Good collaboration between primary care veterinarians, medicine and surgery specialists is necessary for the management of affected cats. Despite the promising results with interventional procedures, owners also need to understand possible short and long-term complications of these interventions.
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2. Berent AC, Weisse CW, Todd K, Bagley DH. Technical and clinical outcomes of ureteral stenting in cats with benign ureteral obstruction: 69 cases (2006–2010). J Am Vet Med Assoc. 2014;244(5):559–576.
3. Wilson DR. Renal function during and following obstruction. Annu Rev Med. 1977;28:329–339.
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11. Kulendra NJ, Syme H, Benigni L, Halfacree Z. Feline double pigtail ureteric stents for management of ureteric obstruction: short- and long-term follow-up of 26 cats. J Feline Med Surg. 2014;16(12):985–991.
12. Berent A, Weisse C, Bagley D, eds. Subcutaneous ureteral bypass device placement for benign ureteral obstruction in cats: 137 cats (174 ureters). In: Proceedings of the American College Veterinary Internal Medicine; 2016.
13. Wolff EDS, Dorsch R, Knebel J, Duffy DJ, Freeman LJ, Guptill L, et al., eds. Initial outcomes and complications of the subcutaneous ureteral bypass procedure at two university hospitals (2012–2015). Proceedings of the American College Veterinary Internal Medicine; 2016.